Avaliação do desempenho da soldagem do aço AISI 444 em aplicações de revestimento de torres de destilação

• Ano de defesa: 2004
• Autor(a) principal: Guimarães, Rodrigo Freitas
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Palavras-chave em Português: Ciência dos materiais; Corrosão; Aço inoxidável
• Link de acesso: http://www.repositorio.ufc.br/handle/riufc/16194

The high sulfur content of oil processed in the refining units attack the "clad" steel AISI 405 or 410S, exposing the structural steel to the corrosive medium. The recovery of the eroded region is made by applying a "lining" of AISI 316L steel. Although steel AISI 316L ensure good corrosion resistance naphthenic, cracks appear in the heat affected zone of the weld (HAZ) after a certain period of operation of the unit, metallurgical problems associated with the HAZ and the efforts of expansion and contraction of conjnto " lining "of the tower and wall. An alternative would be the application of a "lining" of AISI 444 steel having corrosion resistance comparable to the AISI 316L steel and the thermal expansion coefficient closer to the coefficient of the material itself of the tower. However, are not yet known effects on the performance of the steel in the conditions of operation of the tower. In this work we studied the feasibility of applying a "lining" steel AISI 444 for the recovery of the distillation tower to replace the steel AISI 316L. Thus, we evaluated the conditions of embrittlement of AISI 444 in the maximum temperature of the tower (about 400 ° C) and temperature of 475 ° C, by measuring the Brinell hardness and Charpy impact test-V. Specimens of AISI 444 and AISI 316L welded onto steel plates ASTM A516 Gr60 were subjected to thermal fatigue cycles and after each cycle (20 in all), passed an inspection to check for cracks. Soon after it was made microstructural characterization of ZAC. Also samples were taken after the thermal fatigue tests in order to undergo treatment in oil at a temperature of 300 ° C. After treatment in oil, the samples underwent an evaluation in the scanning electron microscope. Were measured masses of the samples before and after treatment in oil to determine the weight loss caused by the corrosive environment. The results indicate that the subjection of the AISI 444 steel to thermal treatment at temperatures 400-475 ° C, causes embrittlement of the same and increasing the temperature of transition ductile brittle to values ​​above 30 ° C but below 60 ° C. The AISI 316L and AISI 444 do not exhibit cracks after the tests and Thermal Fatigue or after treatment in oil. The use of steel AISI 444 may represent a cost savings in the charts of distillation towers since it showed the lowest corrosion rates than steel AISI 316L.